Mal de debarquement syndrome (MdDS) is an illusionary sensation of rocking, with symptoms that include disorientation, imbalance, headache and fatigue. While MdDS most often occurs after an ocean cruise, other forms of transportation can also cause it. The symptoms of MdDS can be transient (minutes) or persistent (years). At this time, neither the mechanisms nor treatment options for this condition exist. We propose that MdDS is triggered by unusual motion, where the rotation in one plane is coupled to the other. We also believe that there is a specific frequency of the stimulus that causes this unusual adaptation. These postulates can be tested by studying the characteristic responses of vestibular system. Our preliminary data has demonstrated that there are distinctive vestibular eye movements in MdDS patients, which are only apparent after experiencing the unusual motion. Furthermore, the frequency of rocking sensation in our patients is 0.2 Hz, which is also a critical frequency for provoking maximum motion sickness in normal population. With the determinants of eye movement and rocking frequency, we can design an effective treatment stimulus for MdDS patients with vestibular and visual interaction. Based on the results of our preliminary treatment, this method is robust. The aim of our proposal is to characterize the vestibular responses of MdDS patients and treat this devastating malady using the findings. We believe that our proposed study will provide new insights into a mysterious phenomenon that has been recognized since Darwin's age, and create a tangible treatment option for those affected by it. PUBLIC HEALTH RELEVANCE: Mal de debarquement syndrome (MdDS) is the rocking sensation after a cruise that can persist for years. There has been no known mechanisms and cure. The proposal is to study the mechanisms and treatment of MdDS.